Laccases (E.C. 1.10.3.2) are enzymes that catalyse the oxidation of a substrate (an electron or hydrogen donor) with oxygen. Such enzymes are known from microbial, plant and animal origins, e.g. from fungi. They are typically copper proteins, i.e. they contain a copper atom or atoms as a prosthetic group.
Use of laccases has been suggested e.g. in bleaching of pulp for paper production, in treatment of waste water from pulp production, for improved bleaching in laundry detergents, for dye transfer inhibition during laundering, and for lignin modification, e.g. in particle board production.
The compound 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate), ABTS, supplied by Boehringer Mannheim, is a chromogenic substrate, and a common peroxidase and phenol oxidase assay agent. These enzymes catalyse the oxidation of ABTS by hydrogen peroxide and dioxygen, respectively, producing a greenish-blue colour, which process may be monitored photometrically.
ABTS has been found to form a stable radical cation when oxidized by a laccase enzyme (polyphenol oxidase, EC 1.10.3.2), and has been proposed to act as a redox mediator for oxidation of non-phenolic lignin model compounds Bourbonnais R., Paice M. G.; FEBS Lett (1990) 267 99-102!.
Studies on demthylation and delignification of kraft pulp by a laccase enzyme in the presence of ABTS showed that the extent of partial demethylation by laccase was increased in the presence of ABTS Bourbonnais, R. and Paice, M. G.; Appl. Microbiol. Biotechnol. (1992) 36 823-827!.
Certain oxidizable substrates e.g. metal ions and phenolic compounds such as 7-hydroxycoumarin (7 HCm), vanillin (VAN), and p-hydroxybenzenesulfonate (pHBS), have been described as accelerators or enhancers, able to enhance bleaching reactions (cf. e.g. WO 92/18683, WO 92/18687, and Kato M. and Shimizu S., Plant Cell Physiol. 1985 26 (7), pp. 1291-1301 (cf. Table 1 particular), or Saunders B. C. et al., Peroxidase, London, 1964, p. 141 ff).